BREAKWATER

a barrier built to shelter a harbor or roadstead from the violence of the waves, thus providing safe anchorage for ships. B’s may be in the form of piers having one end connected with the land, or they may be placed acro the entrance to a bay and completely isolated. They must be of the strongest po ible construction in order to withstand the pre ure of the waves, which has been known to attain a force equivalent to 3% tons per sq. foot, as registered by the dynamometer. Huge blocks of masonry have been literally quarried out of the faces of breakwaters, and ma es of concrete weighing 2,000 tons have been moved from their foundations. The foundation of a b. usually consists of a mound of rough stones, or rubble. The superstructure may consist of a masonry wall built of comparatively small blocks and faced with granite, or it may be formed of huge concrete blocks weighing 50 or more tons. One great drawback to a wall of small blocks is that during its construction the unfinished end is very liable to be shattered by storms. The concrete now in general use consists of a mixture of Portland cement and broken stone and sand. The blocks are made by pouring the mixture into boxes with movable sides, the sides being removed when the concrete sets. The blocks are laid in position by steam cranes, the largest of which are capable of laying 50-ton blocks anywhere within a radius of 100 feet. The blocks are brought to the required position in barges, and as they are lowered by the crane are accurately adjusted by divers. The foundation of a b. may also be formed of large bags of liquid concrete, which rapidly hardens under water. Blocks are sometimes formed on the spot where they are to remain by depositing the concrete liquid in cases. Additional blocks may be deposited round the foot of a b., forming what is called the ‘apron.’